Conventionally, there have been proposed a wide variety of tire pressure drop alarming apparatuses for signaling an abnormal pressure drop for a pneumatic tire. One type of apparatus comprises a resonator attached to the outerside of a rim flange of a wheel rim which includes a vertical portion substantially perpendicular to a rotational axis of the tire and a parallel portion integrally formed with the radially outer end of the vertical portion and in parallel with the rotational axis of the tire. In general, there are many different rim flange forms of the wheel rim depending upon its kind and not produced accurately on the basis of Japanese Industrial Standards so that if the conventional resonator is attached to the rim flange, the characteristic such as resonance frequency and sensitivity Q of the resonator receives effects from the rim flange and is thus fluctuated depending upon its position. In this instance, it is impossible for the resonator to receive magnetic energy from an oscillation coil provided on a body of a car so that the alarming apparatus can not alarm the abnormal pressure drop if it occurs. On the other hand, the resonator attached with a usual balance weight is easily separated from the outside wall of the wheel rim owing to deflection of the tire, vibration of the wheel rim, and centrifugal force acting on the resonator while the car is moving, or otherwise suddenly scattered at an extremely high accelation speed so that it is extremely dangerous for adjacent cars and human bodies.
It is therefore an object of the present invention to provide a tire pressure drop alarming apparatus which can retain a constantly stable characteristic of a resonator to be attached to a wheel rim regardless of the different kinds of the wheel rim and the attachment position to the wheel rim of the resonator.
It is another object of the present invention to provide a tire pressure drop alarming apparatus wherein the resonator is firmly attached to the outside of the rim flange to prevent dangers caused by separation and scattering of the resonator from the rim flange.
The above and other ojects, features and advantages of the present invention will become clear from the following particular description of the invention and the appended claims, taken in conjunction with the accompanying drawings which show by way of example a preferred embodiment of the present invention.